1. Field of the Invention
The present invention relates to a reducer of an electric power steering apparatus and, more particularly, to a reducer of an electric power steering apparatus in which a worm shaft is elastically supported by an elastic member in a direction of a worm wheel to compensate for spacing between the worm shaft and the worm wheel, and an elastic force of the elastic member applied to a bearing bush or a worm shaft bearing can be simply adjusted or measured by adjusting or measuring load applied to a supporting member.
2. Description of the Related Art
FIG. 1 is a view illustrating a structure of a conventional electric power steering apparatus.
As shown in FIG. 1, the conventional power steering apparatus 100 includes a steering system 130 extending from a steering wheel 102 to both wheels 126, and an auxiliary power mechanism 140 for providing auxiliary steering power to the steering system 130.
The steering system 130 includes a steering shaft 106, which has one side connected to the steering wheel 102 and rotating along with the steering wheel 102, and the other side connected to a pinion shaft 108 by means of a universal joint 104. Further, the pinion shaft 108 is connected to a rack bar 112 through a rack and pinion mechanism 110, and both ends of the rack bar 112 are connected to wheels 126 through tie rods 122 and knuckle arms 124, respectively.
The auxiliary power mechanism 140 includes a torque sensor 142 for detecting a torque applied to the steering wheel 102 by a driver to output an electric signal in proportion to the detected torque, an electronic control unit 144 for generating a control signal based on an electric signal received from the torque sensor 142, an electric motor 146 for generating auxiliary power based on a control signal received from the electronic control unit 144, and a reducer 150 having a worm and a worm wheel 156 in order to transfer the auxiliary power generated by the electric motor 146 to the steering wheel 106.
Accordingly, in the electric power steering apparatus, the torque generated by a rotation of the steering wheel 102 is transmitted to a rack bar 112 through the rack and pinion mechanism 110, and the auxiliary power generated by the electric motor 146 is transmitted to the rack bar 112 according to the generated torque.
That is, the torque generated by the rotation of the steering wheel 102 and the auxiliary power generated by the electric motor 146 are added up to enable the rack bar 112 to move right and left.
FIG. 2 is a sectional view illustrating the reducer of the conventional electric power steering apparatus.
As shown in FIG. 2, the reducer 150 includes a worm shaft 254 on which a worm 152 is formed, worm shaft bearings 257 mounted on both ends of the worm shaft 254 respectively to support the worm shaft 254, a plug bolt 210 disposed between a damping coupler 240 and a worm shaft bearing 257 in order to prevent the worm shaft bearings 257 from being spaced in an axial direction of the worm shaft 254, and a plug nut 220 for fixing the plug bolt 210.
The worm shaft 254 is connected to a shaft 290 of the electric motor by means of the damping coupler 240, which is rotated by a driving of the electric motor 146.
The worm wheel 156 is disposed on a side of an outer periphery of the worm 152 and is tooth-engaged with the worm 152 formed on the worm shaft 254. The worm wheel 156 is mounted on the steering shaft 106 which transmits a rotation force of the steering wheel 102 operated by the driver, and transmits the rotation force of the worm shaft 254 generated by the electric motor 146 to the steering shaft 106.
A gear housing 260 has the worm 152, the worm wheel 156 and the like disposed therein, the electric motor 146 is mounted on a side of the gear housing 260 to provide a driving force to the worm shaft 254, and a motor cover 230 combined with the electric motor 146 is coupled with the gear housing 260 by means of a bolt 250.
The worm shaft bearing 257 has a structure in which balls 258 are interposed between an inner race 280 and an outer race 270, and supports a rotation of the worm shaft 254 connected to the electric motor 150 at an end portion of the gear housing 260.
The reducer of the electric power steering apparatus having the above described structure controls a driving of the electric motor by means of the electronic control unit provided to a vehicle according to a driving status of the vehicle. The rotation force of the worm shaft is added to the rotation force of the steering wheel operated by the driver, and is transmitted to the steering shaft, thereby smoothly and stably maintaining the steering status of the driver.
However, in the reducer of the conventional electric power steering apparatus, the worm and the worm wheel rotated by the driving of the electric motor cause friction, thereby increasing spacing between the worm and the worm wheel due to an abrasion. The spacing causes a generation of noise and also has a problem in that an auxiliary steering force assisting a force of operating the steering wheel by the driver is not accurately provided.